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    Re: iSCSI: same ISID



    
    Eddy,
    The purpose here is not what you are looking at.
    
    First, the Target iSCSI (SCSI) Port can inspect all the session arriving at
    its Portal Group, to see if any have the same Initiator name and ISID as
    another one.  If so, it is Not Logged-in.  This would be parallel Sessions
    from the same initiator.
    
    Second, when an Initiator comes back after a failure, they should use the
    same ISID they had previously, thereby permitting approprate Nexus to be
    continued e.g. Persistent Reserves, etc.
    
    The second point was the primary reasons for the Conservative reuse.
    Before this statement, some folks were using a different ISID for each
    Target Node with which they were working.  Then the ISID space could get
    used up, and then as sessions were stopped and restarted, they would
    retrieve an ISID from an available pool of ISIDs, and as a result, the
    approprate Nexus could not be re-established.  Hence the words Conservative
    Reuse means you keep reusing the same ISID number as often as possible.
    
    Therefore, you will probably see an individual Initiator have only 1 ISID,
    ever used.  It is only when a Wedge Driver of some type permits Multiple
    Initiators from the same Host, that you are likely to see the same
    Initiator Name, and Different ISID.  But Still, into any one portal group
    and Target iSCSI (SCSI) Port there will only be one active "Initiator Name
    + ISID" entity.  Each unique "Initiator Name + ISID" are treated (today) as
    if they are as different as if they came from different hosts.
    
    .
    .
    .
    John L. Hufferd
    Senior Technical Staff Member (STSM)
    IBM/SSG San Jose Ca
    Main Office (408) 256-0403, Tie: 276-0403,  eFax: (408) 904-4688
    Home Office (408) 997-6136, Cell: (408) 499-9702
    Internet address: hufferd@us.ibm.com
    
    
    "Eddy Quicksall" <Eddy_Quicksall@ivivity.com>@ece.cmu.edu on 12/20/2001
    10:39:27 AM
    
    Sent by:    owner-ips@ece.cmu.edu
    
    
    To:    "ips@ece. cmu. edu \(E-mail\)" <ips@ece.cmu.edu>
    cc:
    Subject:    iSCSI: same ISID
    
    
    
    
    
    Section 9.1.1 says:
    
    
    
     the same ISID should be used in the Login process to multiple
    
     target portal groups (of the same iSCSI Target or different iSCSI
    
     Targets).  Note that the ISID RULE (2.5.3) only prohibits reuse to
    
     the same target portal group.  It also does not "preclude" reuse to
    
     other target portal groups.
    
     The principle of conservative reuse "encourages" reuse to other
    
     target portal groups.  When a SCSI target device sees the same
    
     (InitiatorName, ISID) pair in different sessions to different target
    
     portal groups, it can identify the underlying SCSI Initiator Port on
    
     each session as the same SCSI port (in effect, it can recognize
    
     multiple paths from the same source).
    
    
    
    This is good but the target will still have to sort out ISID's when they
    
    are different under the same situations named above. So, since the
    
    target still has to have all the code to sort this out, what good is
    
    this statement?
    
    
    
    I think the only thing keeping us from saying you MUST use the same
    
    ISID's is the fact that we have allowed an iSCSI Initiator to have more
    than
    
    one session to the iSCSI Target Portal Group. Is that really necessary? If
    not,
    
    then we could make this a MUST and simplify the target code.
    
    
    
    Eddy
    
    
    
    
    
    


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Last updated: Fri Dec 21 02:17:47 2001
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